U.S. patent application number 14/731032 was filed with the patent office on 2015-12-10 for component including two semiconductor elements between which at least two hermetically tightly sealed cavities having different internal pressures are formed and method for manufacturing such a component.
The applicant listed for this patent is Robert Bosch GmbH. Invention is credited to Jullian Gonska, Friedjof HEUCK, Reinhard Neul, Heiko Stahl, Lars Tebje.
Application Number | 20150353346 14/731032 |
Document ID | / |
Family ID | 54706475 |
Filed Date | 2015-12-10 |
United States Patent
Application |
20150353346 |
Kind Code |
A1 |
HEUCK; Friedjof ; et
al. |
December 10, 2015 |
Component including two semiconductor elements between which at
least two hermetically tightly sealed cavities having different
internal pressures are formed and method for manufacturing such a
component
Abstract
For the targeted influencing of the internal pressure within a
cavity between two elements of a component, a getter material or an
outgassing material is situated in an additional cavity between the
two elements. After the two elements are bonded to one another, the
additional cavity is still to be joined via a connecting opening to
the cavity. The getter material or the outgassing material is then
activated so that gasses are bound in the additional cavity and in
the connected cavity, or an outgassing takes place. Only when the
sought internal pressure has established itself in the connected
cavity is the connecting opening to the additional cavity closed.
In this way, the getter material or the outgassing material is only
used for establishing a defined internal pressure, but no longer
has any influence on the internal pressure within the cavity during
ongoing operation of the component.
Inventors: |
HEUCK; Friedjof; (Stuttgart,
DE) ; Tebje; Lars; (Reutlingen, DE) ; Stahl;
Heiko; (Reutlingen, DE) ; Gonska; Jullian;
(Reutlingen, DE) ; Neul; Reinhard; (Stuttgart,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Robert Bosch GmbH |
Stuttgart |
|
DE |
|
|
Family ID: |
54706475 |
Appl. No.: |
14/731032 |
Filed: |
June 4, 2015 |
Current U.S.
Class: |
257/415 ;
438/51 |
Current CPC
Class: |
B81B 7/02 20130101; B81C
1/00285 20130101; B81B 2203/0315 20130101; H01L 21/50 20130101;
H01L 2224/48463 20130101; B81B 7/0038 20130101; B81C 2203/0145
20130101; H01L 23/10 20130101; H01L 23/02 20130101 |
International
Class: |
B81B 7/00 20060101
B81B007/00; B81C 1/00 20060101 B81C001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 6, 2014 |
DE |
10 2014 210 857.8 |
Claims
1. A component comprising: at least two semiconductor elements
connected to one another via at least one structured connecting
layer; wherein at least two hermetically tightly sealed cavities
are formed between the at least two semiconductor elements, and
different defined internal pressures prevail in the at least two
hermetically tightly sealed cavities, and wherein at least a first
one of the cavities is sealed by a circumferential bonding frame in
the connecting layer, and wherein at least a second one of the
cavities is at least partially sealed by a welding joint between
the at least two semiconductor elements.
2. The component as recited in claim 1, wherein a semiconductor
material of at least one of the two semiconductor elements is
included in the welding joint.
3. The component as recited in claim 2, wherein a metallic coating
of least one of the two semiconductor elements is involved in the
welding joint.
4. The component as recited in claim 2, wherein the welding joint
closes a connecting opening to an additional, hermetically tightly
sealed cavity between the two semiconductor elements, and one of a
getter material or an outgassing material is situated in the
additional, hermetically tightly sealed cavity.
5. A method for manufacturing a component having at least two
semiconductor elements connected to one another in such a way that
at least two hermetically tightly sealed cavities are formed
between the two semiconductor elements, in which cavities different
defined internal pressures prevail, the method comprising:
providing at least one of the two surfaces of the two semiconductor
elements to be joined with at least one structured connecting
layer; and subsequently establishing a bond connection between the
two semiconductor elements via the structured connecting layer,
wherein at least one of the two cavities is hermetically tightly
sealed at a predefined ambient pressure; providing at least one
additional cavity; providing at least one of the two surfaces of
the two semiconductor elements to be joined with one of a getter
material or an outgassing material in the area of the additional
cavity; structuring at least the connecting layer in such a way
that at least one connecting opening as a pressure connection is
provided between the additional cavity and at least one connected
cavity after the establishing of the bond connection; activating
the one of the getter material or the outgassing material after
establishing the bond connection so that gasses in the additional
cavity and the connected cavity are bound or an outgassing takes
place; and closing the connecting opening when the sought internal
pressure has been established in the at least one connected
cavity.
6. The method as recited in claim 5, wherein the connecting opening
is closed in a laser welding process with the aid of an infrared
laser.
7. The method as recited in claim 6, wherein a hermetically tight
welding joint is established in the laser welding process between
the semiconductor materials of the two element surfaces to be
joined by melting the semiconductor materials of the two element
surfaces.
8. The method as recited in claim 5, wherein: an eutectic bond
connection is established between the two semiconductor elements
by: (i) applying and structuring at least one bonding layer on both
of the two element surfaces to be joined; and (ii) a hermetically
tightly sealed welding connection between the semiconductor
material of the one element surface to be joined and the bond
material on the other element surface is established during the
laser welding process.
9. The method as recited in claim 5, wherein at least one of the
two surfaces of the two semiconductor elements to be joined is
structured in order to produce recesses for at least one of (i) the
at least two cavities and (ii) the at least one additional
cavity.
10. The method as recited in claim 5, wherein: the two
semiconductor elements are each produced in a wafer composite; the
bonding connection between the two semiconductor elements is
established in the wafer composite; the subsequent closure of the
connecting opening takes place in the wafer composite; and the at
least one additional cavity is situated in the border area of the
component so that the at least one cavity is separated when
separating the component.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a component including at
least two semiconductor elements which are connected to one another
via at least one structured connecting layer, at least two
hermetically tightly sealed cavities, in which different defined
internal pressures prevail, being formed between these two
elements. At least one of those cavities is sealed by a
circumferential bonding frame in the connecting layer. Moreover,
the present invention relates to a method for manufacturing such a
component.
[0003] 2. Description of the Related Art
[0004] One important exemplary application for the components
mentioned here are so-called IMUs (inertial measurement units)
including a MEMS (microelectromechanical system) element which
includes a rotation rate sensor component as well as an
acceleration sensor component. The two sensor components are formed
in the layer structure of the MEMS element and situated next to one
another. They are capped with the aid of the second element in
order to protect the sensor structures and to ensure defined
pressure conditions for the respective sensor operation. Since
rotation rate sensors and acceleration sensors are usually operated
at different ambient pressures, an individual cap structure is
provided in the second element for each sensor structure. In
rotation rate sensors, a part of the sensor structure is driven
resonantly. In order to keep the damping of the sensor structure
preferably low, a preferably low internal pressure of approximately
1 mbar is set in the cavity of a rotation rate sensor element. The
rotation rate sensor may then be operated even at a relatively low
excitation voltage. In contrast thereto, the sensor structure of an
acceleration sensor is to preferably not be excited to vibrations.
For this reason, acceleration sensors are operated at a
significantly higher internal pressure of typically 500 mbar.
[0005] The internal pressure which results within a cavity between
two elements joined by bonding is a function of the ambient
pressure at which the bonding process is carried out. For this
reason, the implementation of cavities having a different internal
pressure for the individual sensor components of a MEMS element
requires special measures when the two, sensor components are to be
capped only with another element and in one single bonding
step.
[0006] This is the object on which US patent application
publication 2012/0326248 A1 is based. In this publication, it is
suggested, among other things, to provide, in the area of a cavity,
one of the element surfaces to be joined with a getter material or
an outgassing material which bonds or releases a defined amount of
gas at a corresponding temperature treatment. In this way, a
targeted decrease or increase of the internal pressure of the
cavity is to be effectuated.
[0007] This procedure is problematic for multiple reasons. In
practice, it has been found that the internal pressure in such a
cavity often changes even after the sensor calibration, since the
getter material post-getters or the outgassing material gasses out
further. This ultimately results in a distortion of the measurement
results. But the micromechanical sensor function is often also
interfered with by the extraneous materials in the cavity. Material
ruptures repeatedly occur in particular in getter layers. This
results in individual particles breaking off, which settle in or at
the sensor structure and whose mobility is limited.
BRIEF SUMMARY OF THE INVENTION
[0008] With the present invention, the known use of getter
materials and outgassing materials for the targeted influencing of
the internal pressure within a cavity between two elements is
further developed in that these materials are only used for setting
a defined internal pressure, but no longer have any influence on
the internal pressure within the cavity during ongoing operation of
the component.
[0009] This is achieved according to the present invention by the
getter material or the outgassing material being situated in an
additional cavity between the two elements, this additional cavity
being connected after the bonding process via a connecting opening
with at least one of the cavities to be sealed. The getter material
or the outgassing material is, activated after the establishment of
the bond connection so that gasses are bound in the additional
cavity and the connected cavity, or an outgassing takes place. Only
when the sought internal pressure has established itself in the
connected cavity is the connecting opening to the additional cavity
closed, preferably in a laser welding process.
[0010] Therefore, at least one of the cavities of the component
according to the present invention is sealed via a circumferential
bonding frame in the connecting layer between the two elements,
while at least one other cavity of the component according to the
present invention is at least in areas sealed using a welding joint
between the two elements.
[0011] According to the present manufacturing method, at least one
further cavity is provided in addition to the at least two cavities
which are to be sealed between the two elements, for example, by
creating another cavity recess in at least one of the two element
surfaces, or wafer surfaces, to be joined. At least one of the two
surfaces to be joined is then provided with a getter material or an
outgassing material in the area of this additional cavity.
Furthermore, the connecting layer is structured in such a way that
at least one cavity is hermetically tightly sealed after the
bonding process and that there is at least one connecting opening
as pressure connection between the additional cavity and at least
one further cavity to be sealed. After establishing the bond
connection, the getter material or the outgassing material is
activated so that gasses are bound in the additional cavity and in
the connected cavity, or an outgassing takes place. Only when the
sought internal pressure has established itself in the connected
cavity is the connecting opening closed.
[0012] This procedure according to the present invention enables
the implementation of multiple, hermetically tightly enclosed
cavities between two elements having different defined internal
pressures. The internal pressure which has established itself after
the bonding process for joining the two elements within the
cavities is decreased or increased in a defined way in at least one
of the cavities with the aid of a getter material or an outgassing
material, this material not being situated in the cavity itself,
however, but in an additional cavity. This cavity is connected to
the cavity to be influenced via a connecting opening. The internal
pressure set in this way is then "frozen" by decoupling the
additional cavity having the getter material or the outgassing
material. For this purpose, the connecting opening is closed. In
this way it is not only prevented that the internal pressure of a
cavity changes retroactively due to uncontrolled post-gettering or
outgassing, but also that particles of the extraneous material,
i.e., of the getter material or of the outgassing material,
influence the component functions.
[0013] As mentioned above, the connecting opening is preferably
closed in a laser welding process using an infrared laser. Since
semiconductor materials, such as, for example, silicon, are
transparent to light in the infrared spectrum, an infrared laser
beam may be focused easily through the semiconductor material in
the area of the connecting surface between the two semiconductor
elements. In this way, the semiconductor material may be partially
melted, in this area, but also a metallic coating of the element
surface [may be partially melted].
[0014] In this way, the hermetically tight welding joint may also
be established between the semiconductor materials of the two
element surfaces to be joined or also between the semiconductor
material of the one component surface to be joined and a metallic
coating on the other element surface. When the two elements are
joined with one another using eutectic bonding, one of the two
bonding layers may easily be used as a metallic coating for the
laser welding. For this purpose, the two bonding layers have to
only be structured in a suitable way in the area of the connecting
opening.
[0015] Generally, micromechanical structures and/or electronic
circuit elements, which are to be capped, are formed in the surface
of the one element. For this purpose, the surface of the other
component is often structured in order to implement cap recesses
for the individual function elements. Advantageously, at least one
depression is created as an additional cavity recess. This cavity
recess may have a different depth than the cavity recesses. When
the getter material or the outgassing material is to be applied to
the structured cap bottom side, it is advantageous to not form the
depression for the additional cavity too deeply, since the material
may then be deposited and structured using standard processes.
[0016] Depending on the design, the additional, hermetically
tightly sealed cavity having the getter material may remain in the
structure of the component according to the present invention or it
may also be separated from the structure.
[0017] Generally, such components are manufactured in the wafer
composite. For this purpose, the two elements are each produced in
the wafer composite, the bond connection between the two elements
is produced in the wafer composite and also the subsequent closing
of the connecting opening takes place in the wafer composite. When
the at least one additional cavity is situated in the border area
of the component, it may be easily separated when separating the
component. This proves to be particularly advantageous in
particular with regard to a preferably extensive miniaturization of
the components since no chip surface has to be reserved for the
additional cavity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1a schematically shows a cross-sectional view of MEMS
element 10 and of cap element 20 of a component 100 according to
the present invention after the bonding step.
[0019] FIG. 1b schematically shows a cross-sectional view of this
component 100 during laser welding for closing the connecting
opening.
DETAILED DESCRIPTION OF THE INVENTION
[0020] FIGS. 1a and 1b show the connecting concept according to the
present invention with which multiple cavities having different
defined internal pressures may be hermetically tightly sealed
between two elements of a component.
[0021] Component 100 shown in FIGS. 1a and 1b includes a MEMS
element 10, in whose layer structure two micromechanical structures
11 and 12, which are independent from one another, are formed.
These may be, for example, sensor structures, such as an
acceleration sensor structure and a rotation rate sensor structure,
or also micromechanical actuator structures. The two
micromechanical structures 11 and 12 are each situated next to one
another and also spatially separated from one another by a frame
structure 13 in the layer structure.
[0022] A second element 20, which acts as a cap for the two
micromechanical structures 11 and 12, is mounted on the layer
structure of MEMS element 10. For this purpose, two cap recesses 21
and 22 are formed in the cap bottom side, which are dimensioned and
situated according to the micromechanical structures 11 and 12 of
MEMS element 10. Between these two cap recesses 21 and 22, a
further additional depression 23 is situated on the cap bottom
side, into which a getter material 25 was deposited. The depression
having this getter material 25 is positioned above MEMS frame
structure 13. It should be noted here that instead of the getter
material, an out-gassing material might be situated in depression
23.
[0023] FIG. 1a shows component 100 after cap element 20 was mounted
in a bonding process onto the structured surface of MEMS element
10. The connection between MEMS element 10 and cap element 20 was
established in the exemplary embodiment illustrated here using a
connecting layer 30, for example, made of glass solder. From this
connecting layer 30, a bonding frame structure was structured out
which includes a circumferentially closed bonding frame 31 for
micromechanical structure 11 and cavity recess 21 and which
hermetically tightly seals corresponding cavity 1 between MEMS
element 10 and cap element 20. The bonding frame structure also
includes a bonding frame 32 for micromechanical structure 12 and
cavity recess 22, which is, however, not closed circumferentially.
Therefore, there is a pressure connection between corresponding
cavity 2 and a further cavity 3, which is enclosed between MEMS
framing structure 13 and cap depression 23. The bonding frame
structure is designed in such a way that cavities 2 and 3 are
together hermetically tightly sealed and are only connected to one
another via a connecting opening 33 in the bonding frame structure.
This connecting opening 33 must ensure a pressure connection
between the two cavities 2 and 3. For this purpose it may be
punctiform or it may also extend across a wider surface. In
addition, multiple connecting openings may also be provided.
[0024] The bond connection between the two elements 10 and 20 may
alternatively also be established using a eutectic bonding process,
a thermocompression bonding process, or any other bonding process.
In this case, the two element surfaces to be joined are provided
with structured bonding layers which then form a eutectic
connection during the bonding process.
[0025] Internal pressure p0 prevailing in cavity 1 essentially
corresponds to the ambient pressure which was selected for the
bonding process. A significantly lower internal pressure p1
prevails in cavities 2 and 3. This is due to the fact that getter
material 25 was activated after establishing the bond connection so
that it bound a defined gas volume within cavities 2 and 3. For
this purpose, getter material 25 was heated in a targeted manner,
for example, with the aid of an infrared laser. The use of an
infrared laser enables a locally limited heating of component 100
only in the area of the getter material so that heat-sensitive
component parts, such as, for example, circuit components or the
organic coating of a micromechanical structure, are protected.
[0026] After sought internal pressure p1 has established itself in
the two cavities 2 and 3, cavity 3, including getter material 25,
is separated from cavity 2 by closing connecting opening 33. This
is illustrated in FIG. 1b. Closure 35 is here produced by welding
using an infrared laser 40. For this purpose the infrared laser
beam is focused through the semiconductor material of cap element
20 onto the area of connecting opening 33. In this way, the
semiconductor material of the two element surfaces is in this area
melted within a locally limited area until it joins and the two
cavities 2 and 3 are hermetically tightly sealed separately from
one another. An internal pressure p1 now prevails in the two
cavities 2 and 3. Since cavity 2 is free of getter material,
internal pressure p1 may also not change here due to post-gettering
or uncontrolled outgassing.
[0027] The exemplary embodiment described above shows that the
pressure within a cavity, which is hermetically tightly sealed in a
bonding process between two components, is, on the one hand, a
function of the ambient pressure during the bonding process, but,
on the other hand, is also a function of whether a getter material
or an outgassing material is enclosed in the cavity. The volume of
the bound or released gas is a function of the size of the
absorbing or outgassing surface and is a function of the
temperature. The internal pressure in a cavity may therefore be
influenced by the choice of the getter material or the outgassing
material, the size of the absorbing or outgassing surface, and the
temperature curve after sealing of the cavity, the cavity volume
also needing to be taken into account. In this way, the internal
pressure of every individual cavity may be set individually.
* * * * *